<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>test page</title>

    <style>
      #box {
        width: 50px;
        height: 50px;
        background-color: blue;
        position: absolute;
        left: 0;
        top: 50%;
        transform: translateY(-50%);
      }
    </style>
  </head>

  <body>
    <div style="width: 200px; height: 200px; background: #09c"></div>
    <div id="red" style="width: 200px; height: 200px; background: red"></div>

    <div id="box"></div>
  </body>
</html>
